The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art.
Many motor vehicles use torque converters in order to provide a fluid coupling between the output of an engine and the input of a transmission in order to multiply torque when there is a substantial difference between input and output rotational speeds, thereby providing the equivalent of a reduction gear. The process of selecting a torque converter for a specific engine-transmission combination begins with an evaluation of the stall turbine torque and the converter speed ratio of the torque converter at the engine's full load governed speed with respect to the transmission's ratings. The traditional approach has been to optimize vehicle performance, and thus the recommended torque converter is the one which provides the maximum turbine torque while not exceeding these ratings. An additional consideration involves the engine's ability to accelerate from idle against the stall capacity of the torque converter. Many of the current commercial diesel engines are limited in their ability to generate enough torque at low speed to accelerate properly from idle stall when the vehicle is operating near its gross vehicle rating. This issue results in the use of lower capacity torque converters. Also, the increasing emphasis on fuel economy has resulted in more interest in the use of higher capacity torque converters.
Accordingly, there is a need in the art for a method for controlling a transmission during acceleration from idle that reduces the effective stall capacity of the torque converter in order to allow the engine to accelerate to a speed where it can generate sufficient torque to adequately accelerate the vehicle. This method will allow the use of higher capacity torque converters in a given engine-transmission combination, thereby resulting in improved fuel economy and vehicle performance.